1. Field of the Invention
The present invention is related to a base station transmission system in a mobile communication system, and more particularly, to a base station transmission system in a CDMA (Code Division Multiple Access) mobile communication system and a method for processing a baseband signal using the same, which can provides a baseband signal less susceptible to noise and maximize a channel capacity.
2. Background of the Related Art
In general, in the mobile communication system, there are transmission or reception signal of baseband, intermediate frequency band, and radio frequency band depending on a frequency band of the signal. The baseband is a frequency band occupied by an original information signal before modulation. Therefore, the baseband is a frequency band of which lowest frequency is near to 0 or containing a direct current component. The intermediate frequency band is a frequency band to which a baseband frequency to be transmitted to outside of the station is increased by adding a local oscillator frequency in a frequency converter in a base station and, opposite to this, to which a radio frequency received from outside of the station is decreased by subtracting the local oscillator frequency in the frequency converter. The radio frequency band is a frequency band for use in radio communications within an electromagnetic spectrum range from 10 KHz to 300 GHz.
FIG. 1 illustrates a block diagram showing a related art basestation transmission system in a CDMA mobile communication system.
Referring to FIG. 1, the related art basestation transmission system in a CDMA mobile communication system is provided with a channel card unit 1, a buffer unit 2, and a baseband signal processing unit 3, each of which has a PCB form. The channel card unit 1 is provided with four CDMA modem 11xcx9c14, each having a CDMA basestation modem unit 10 for band spreading a received digital voice signal according to a CDMA recommendations(for example, IS-95 family), a digital combining unit 20a or 20b for combining digital signals from the CDMA basestation modem unit 10 transmitted through alpha, beta, gamma paths, a digital/analog converting unit 30a or 30b for converting the digital signal from the digital combining unit 20a or 20b into an analog signal, a low pass filter 40a and 40b for removing unnecessary frequency band in view of a signal characteristic from the signal from the digital/analog converter 30a or 30b, and an amplifier 50a or 50b for amplifying a signal from the low pass filter 40a or 40b to a required level. The buffer unit 2 is provided with amplifiers 61xcx9c66 equal to the channel card units 1 in number, each for separating analog signals provided through I, and Q channels from the amplifier 50a or 50b into sectors of alpha, beta, and gamma. The baseband signal processing unit 3 is provided with accumulators 70axcx9c70f each for accumulating an analog signal from the buffer amplifier 61xcx9c66, phase equalizers 80axcx9c80f each for regulating a phase characteristic of a signal from the accumulator 70axcx9c70f to suit to a CDMA signal characteristic, low pass filters 90axcx9c90f each for removing an unnecessary frequency band from a signal from the phase equalizer 80axcx9c80f to satisfy a cut offset characteristic, and intermediate amplifiers 100axcx9c100f each for receiving a signal from the low pass filter 90axcx9c90f and amplifying to a required level for easy modulation in I and Q modulation type(one of QPSK modulation type). The back planes 110a and 110b in FIG. 1 denote unitary PCBs, which is one of transmission mediums used in place of cable in data transmission between the channel card unit 1, the buffer unit 2 and the baseband signal processing unit 3, each in a PCB form, in the basestation transmission system. As shown in FIG. 1, output terminals on the channel card unit 1 are connected to the back plane 110a, and output terminals on the buffer unit 2 are connected to the back plane 110b. 
The operation of the related art basestation transmission system in a CDMA mobile communication system will be explained.
A voice signal encoded in a vocoder is provided to one of the CDMA modem 11xcx9c14 in the voice channel card unit 1 as an 8 bit data bus. Each of the CDMA modems 11xcx9c14, two or four are provided on one board, provides one communication channel. In the related art, the CDMA modem 11 or 14 spreads a voice signal into a digital baseband signal of 1.2288 Mcps, selects I or Q channel, and provides to the digital combining unit 20a or 20b at up to 9600 bps through three channels of alpha, beta, gamma. The digital combining unit 20a or 20b receives the baseband signal split into three alpha, beta, and gamma paths for each of the I and Q channels from one CDMA modem 11 and 14, subjects to digital combining, and provides to the digital/analog converter 30a or 30b in 10 bit units. Then, the digital/analog converter 30a or 30b converts the received digital signal into an analog signal suitable for radio transmission. The low pass filter 40a or 40b removes unnecessary bands in view of a signal characteristic from the analog signal of 1.2288 MHz from the digital/analog converter 30a or 30b. The amplifier 50a or 50b provides the analog signal from the low pass filter 40 or 40b to the buffer amplifier 61xcx9c66 in the buffer unit 2 separate for three alpha, beta, and gamma paths for each of the I and Q channels through the back plane 110a. The buffer amplifier 61xcx9c66 in the buffer unit 2 provides the analog signal to the baseband signal processing unit 3 separate for three alpha, beta, and gamma paths for each of the I and Q channels through the back plane 110b. Each of the accumulators 70axcx9c70f in the baseband signal processing unit 3 accumulates the analog signal from the buffer amplifier 61xcx9c66 and provides to the phase equalizer 80axcx9c80f Each of the phase equalizers 80axcx9c80f adjusts a phase characteristic of a signal from the accumulator 70axcx9c70f to suit to a CDMA signal characteristic and provides to the low pass filter 90axcx9c90f. The low pass filter 90axcx9c90f removes unnecessary bands from the phase adjusted CDMA baseband signal to satisfy a cut offset characteristic and provides to the intermediate amplifier 110axcx9c100f. The intermediate amplifier 100axcx9c100f amplifies the CDMA baseband signal, and then converted into a radio frequency for transmission, and transmitted through a basestation antenna.
However, in the related art CDMA basestation transmission system, the baseband signal is susceptible to noise during the baseband signal provided from the buffer unit 2 through the back plane 100b is accumulated in the accumulator in the baseband signal processing unit 3. This is because the baseband signal provided through the back plane 110b is an analog signal susceptible to noise. The demerit significantly affects a forward capacity of the system, which can be a great cause of a communication quality degradation when the communication is busy. That is, the related art basestation transmission system has a limit in improvement of a communication quality through improvement of a baseband signal characteristic improvement.
A maximum number of the CDMA modems 11xcx9c14 mountable on the channel card unit 1 is four under the present level of a basestation transmission system supporting technique. The basestation transmission system of the Qualcomm in U.S.A. can supports 2 CDMA modems, and the STAREX-CMX of the LG Information and Communication, Ltd. can supports 4 CDMA modems. As one CDMA modem provides on communication channel, the basestation transmission system with the channel card unit, the buffer unit, and the baseband signal processing unit shown in FIG. 1 should be kept extended for an increased transmission rate of the baseband signal. However, the extension results in a complicated structure and connection of entire transmission system, and causes many problems in operation and power control of the transmission system.
Accordingly, the present invention is directed to a base station transmission system in a CDMA mobile communication system and a method for processing a baseband signal using the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a base station transmission system in a CDMA mobile communication system and a method for processing a baseband signal using the same, in which a baseband signal is processed to be less susceptible to noise for improving a communication quality.
Another object of the present invention is to provide a base station transmission system in a CDMA mobile communication system which can extend communication channels provided to one channel card up to 16.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the base station transmission system in a CDMA mobile communication system includes a channel card unit for band spread modulating a received voice signal into a baseband signal and transmitting in series, a digital combining unit for collecting the baseband signals from the channel card unit separate for preset channels, accumulating the baseband signals, and separating the baseband signals for preset channels, a digital/analog converting unit for converting the serial baseband signal from the digital combining part into a parallel signal and then converting into an analog signal, and a baseband transmission processing unit for processing the baseband signal from the digital/analog converting unit to meet the radio signal recommendations, wherein the channel card unit and the digital combining unit are integrated on a PCB and the digital/analog converting unit and the baseband transmission unit are also integrated on a PCB.
In another aspect of the present invention, there is provided a method for processing a baseband signal using a basestation transmission system in a mobile communication system, including the steps of (1) band spread modulating a received voice signal into a baseband signal and transmitting in series, (2) collecting the baseband signals transmitted in series separate for preset channels, accumulating the baseband signals, separating the baseband signals for preset channels again, and transmitting the baseband signals in series, (3) converting the transmitted serial baseband signal into a parallel signal and then into an analog signal, and (4) processing the analog baseband signal to meet the radio signal recommendations.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: